套接字:使用Java发现端口可用性

问题

如何使用Java以编程方式确定给定计算机中端口的可用性?

即给定一个端口号,确定它是否已被使用?


#1 热门回答(84 赞)

这是来自Apachecamel项目的implementation

/**
 * Checks to see if a specific port is available.
 *
 * @param port the port to check for availability
 */
public static boolean available(int port) {
    if (port < MIN_PORT_NUMBER || port > MAX_PORT_NUMBER) {
        throw new IllegalArgumentException("Invalid start port: " + port);
    }

    ServerSocket ss = null;
    DatagramSocket ds = null;
    try {
        ss = new ServerSocket(port);
        ss.setReuseAddress(true);
        ds = new DatagramSocket(port);
        ds.setReuseAddress(true);
        return true;
    } catch (IOException e) {
    } finally {
        if (ds != null) {
            ds.close();
        }

        if (ss != null) {
            try {
                ss.close();
            } catch (IOException e) {
                /* should not be thrown */
            }
        }
    }

    return false;
}

他们正在检查DatagramSocket以检查端口是否可用于UDP和TCP。

希望这可以帮助。


#2 热门回答(36 赞)

对于Java 7,你可以使用try-with-resource来获得更紧凑的代码:

private static boolean available(int port) {
    try (Socket ignored = new Socket("localhost", port)) {
        return false;
    } catch (IOException ignored) {
        return true;
    }
}

#3 热门回答(34 赞)

从Java 7,David Santamaria's answer开始,它似乎不再可靠。但是,看起来你仍然可以可靠地使用Socket来测试连接。

private static boolean available(int port) {
    System.out.println("--------------Testing port " + port);
    Socket s = null;
    try {
        s = new Socket("localhost", port);

        // If the code makes it this far without an exception it means
        // something is using the port and has responded.
        System.out.println("--------------Port " + port + " is not available");
        return false;
    } catch (IOException e) {
        System.out.println("--------------Port " + port + " is available");
        return true;
    } finally {
        if( s != null){
            try {
                s.close();
            } catch (IOException e) {
                throw new RuntimeException("You should handle this error." , e);
            }
        }
    }
}